overloadingg operator

Question

Hello I have this problem: class Person { string name; string surname; public static bool operator ==(Person p1 Person p2) { if (p1.name == p2.name && p1.surname == p2.surname) return true;else return false; } } //main program.. Person p = p.Mysearch(Tim); // if it don't found Tim Mysearch() return null if (p == null) { ......} //problem is here The problem is when I check for p ==null; I have defined == the check p.name and p.surname but null HASN'T any attribute (it isn't a person... How can I solve it problem?? thanks.

Alan · Answer

If you recode that line as follows then no exception will be thrown if p1 is null whether you've overloaded the != operator or not: if (p1 != null && p1.isNotProfessor()) listperson.Add(p1);

Marco · Answer

Hello I just have a similar problem. Can I solve with operator overloading? if ( p1.isNotProfessor()) listperson.Add(p1); Sometimes happen that p1 comes null: so the code on the if crash at runtime. Can I solve it ? thanks.

Alan · Answer

To avoid the == operator being called recursively you need to use the static Object.ReferenceEquals() method to test for null. You also need to override the != operator and to get rid of the compiler wanrings that will otherwise come up you should override the Object.Equals() and Object.GetHashCode() methods as well. Something like this: public static bool operator ==(Person p1 Person p2) { if (Object.Equals(p1 null)) return (Object.ReferenceEquals(p2 null)); else if (Object.ReferenceEquals(p2null)) return (Object.ReferenceEquals(p1null)); else if (p1.name == p2.name && p1.surname == p2.surname) return true; else return false; } public static bool operator !=(Person p1 Person p2) { return !(p1 == p2); } public override bool Equals(object obj) { if (!(obj is Person)) return false; return (this == (Person)obj); } public override int GetHashCode() { return base.GetHashCode(); }